The present invention relates generally to a system and method for locating buried lines such as, for example, pipes, cables, conduits or other conductors and, more particularly, to a locating arrangement that is configured for distinguishing “false” cable locating signals.
The installation of utility lines underground is increasingly popular for reasons of aesthetics and for practical reasons such as, for example, protecting these lines from the effects of severe above ground weather conditions. In areas where buried lines have previously been installed, however, it is often necessary to locate the position of the lines. This task is generally accomplished by causing the line to emit an electromagnetic locating signal by connecting a transmitter arrangement to an electrically conductive component of the line. It is noted that such an electrically conductive component may be provided specifically for this purpose such as, for example, a tracer wire as part of a fiber optic cable. Once the location of the cable or cables in a region has been identified, subsequent operations such as excavation in the region may be performed in a way that avoids pre-existing cable locations. Of course, sufficient locating accuracy is a necessity.
Unfortunately, the prior art has been limited by at least one aspect of the aforedescribed technique. Specifically, the electromagnetic signal that is transmitted from a particular cable of interest can be coupled to another cable in the region. This coupling can take place through the ground or can occur when the cables are in physical contact, for example, at their distal ends whereby a direct, resistance-type electrical connection is formed between the cables. Once the locating signal is coupled to another cable, that cable will re-emit the locating signal. Using prior art systems, the re-emitted locating signal is, in most cases, indistinguishable from the original locating signal. When faced with this situation, it is not uncommon for an operator of an above ground locator to follow a cable that is re-emitting the locating signal, with no indication that a different cable is, in fact, being located. Thus, a considerable amount of confusion is possible when more than one cable is present in the operating region.
The present invention resolves the foregoing limitations in a highly advantageous way, while providing still further advantages, as will be described immediately hereinafter.